Local and global planarization of semiconductor wafers becomes increasingly important as more metal layers and interlayer dielectric layers are stacked on the wafers. A preferred method to planarize semiconductor wafers is the chemical mechanical polishing (CMP) method, where a surface of a semiconductor wafer is polished using a slurry solution supplied between the wafer and a polishing pad. The CMP method is also widely used for damascene process to form copper structures on the semiconductor wafers.
In general, a CMP equipment includes a polishing table where a polishing pad is placed and a wafer carrier that supports a semiconductor wafer and presses the wafer against the polishing pad. The CMP equipment may also include a wafer cleaner to clean and dry the polished wafers.
An important component of a CMP equipment is the polishing head that holds a semiconductor wafer to be polished on a polishing surface. The polishing head is designed to chuck (load) and de-chuck (unload) the wafer, and to apply pressure to the wafer onto the polishing surface. After a wafer is polished, a strong bond may exist between the wafer and the polishing surface, which makes chucking the wafer onto the polishing head challenging. The polishing head must be designed to overcome this bond between the wafer and the polishing surface to chuck the wafer onto the polishing head. During the wafer polishing, the polishing head must apply proper pressure to the wafer to minimize uneven polishing.
In view of the above issues, what is needed is a polishing head and method for handling and polishing semiconductor wafers that overcomes these issues to properly handle and polish the wafers.